This invention relates to a method for establishing an underground well, in particular a petroleum well. By establishing is meant to drill, completely or partially, a hole and further to line the hole, so that the wall of the hole is sealed, and to place a completion string in the well for production or injection. If a hole exists from earlier, the method may also be used in order to line the hole or in order to place a completion string, whereby the possibility for downhole measuring and control is improved.
More particularly, the invention relates to a method, in which a lining is transported into the borehole together with the drilling tool and positioned in the borehole before the drilling tool is pulled to the surface. The method is particularly suitable for use in so-called deviated drilling, in which the direction of the borehole may deviate considerably from a vertical direction.
In addition, the method includes the positioning of a completion string, maybe with integrated electric or optical cables, and possibly with sensors and actuators for completion of the well for production or injection. The invention also includes a device for practicing the method.
In the description, upper and lower refer to relative positions when the tool is in a vertical borehole.
When drilling an underground deviating borehole, it can be difficult to have sufficient thrust transferred to a drill bit. The reason may be that a substantial part of the weight of the drill string and the weight of possible drill collars placed above the drill bit is absorbed by friction between the borehole wall and the drill string. It has turned out that to move casing, for example, forward in a deviation borehole can be difficult when relatively long and approximately horizontal borehole portions are involved. The reason for this is the considerable frictional forces, which arise between the borehole and the casing as the casing is being moved, and which have to be overcome.
Norwegian patent 179261 deals with a device, in which there is arranged, above the drill bit, a piston sealingly movable against the borehole. The fluid pressure in the borehole exerts a force on the piston, which is arranged to move the drill bit into the borehole. The document describes to a limited degree the lining and completion of boreholes.